OBJECTIVES: I. Determine the rate of objective response and disease stabilization in patients with relapsed or refractory multiple myeloma treated with R115777. II. Determine whether the degree of inhibition of FTase activity and farnesylation of lamin-B, H-, K-, and N-RAS in peripheral blood mononuclear cells and tumor tissue correlates with tumor response in patients treated with this regimen. III. Determine whether the presence of activating RAS mutations in myeloma cells predicts treatment response in patients treated with this regimen. IV. Correlate R115777 plasma levels and RAS mutation status with tumor response in patients treated with this regimen.